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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="Description" content="描述">
    <title>Document</title>

    <style>
        body{
            margin:0;
        }
        canvas{
            background:#000;
        }
     </style>
</head>

    <body>
        <canvas id ="canvas" width="500" height="500">您的浏览器不支持canvas标签，请您更换浏览器！></canvas>
        <script> 
            var can = document.getElementById("canvas");
            var ctx = can.getContext("2d");
            var s = window.screen;
            var w = can.width = s.width;
            var h = can.height = s.height;
            <!-- 绘制文本 -->
            var words = Array(256).join("1").split("");  //记录坐标
            function draw(){
                //透明矩形框，覆盖前面，实现渐变效  果 
                ctx.fillStyle = "rgba(0,0,0,0.05)";
                ctx.fillRect(0,0,w,h); //绘制矩形
                //65-90  A-Z  97-122 a-z
                var text = String.fromCharCode(65+Math.ceil(Math.random()*57));  //随机字母
                //console.log(text);
                ctx.fillStyle = "#0f0";  //绿色
                //ctx.fillStyle = color1();  //随机颜色
                words.map(function(y,index){ //数组里面每个元素的一个映射
                    //console.log(index);
                    var x = index*10;
                    ctx.fillText(text,x,y);
                    words[index] = (y > 748 + Math.random()*452)?0:y+10;
                })
            }
            //draw();
            setInterval(draw,100);
            
            //flag{W3lCome_7o_tHe_W0rld_of_CTF!}
        </script>
    </body>

</html>
